Program Highlights

Defect-Assisted Tunneling across Ferroelectric Tunnel Junctions

Konstantin Klyukin, Lingling Tao, Vitaly Alexandrov, and Evgeny Tsymbal  
Nebraska MRSEC

Ferroelectric materials possess switchable electric polarization which makes them useful for novel electronic devices, such as ferroelectric tunnel junctions (FTJs). The latter employ an ultrathin ferroelectric layer between two metal electrodes. This layer is so thin that it allows quantum-mechanical electron tunneling across it. Switching its ferroelectric polarization leads to a significant change in electrical resistance of the FTJ, which makes it useful as a memory element.
Nebraska MRSEC researchers have demonstrated that strontium titanate can be used as a ferroelectric tunnel barrier in these devices. By performing state-of-the-art theoretical modeling, they predicted that titanium atoms substituting strontium form localized electronic states in the energy gap of this material. These antisite defects enhance electron tunneling conductance which strongly depends on ferroelectric polarization orientation. This prediction explains the intrinsic mechanism of electron tunneling across strontium titanate and shows a possibility of using this material in FTJs.

K. Klyukin, L. L. Tao, E. Y. Tsymbal, and V. Alexandrov, “Defect-assisted tunneling electroresistance effect in ferroelectric tunnel junctions,” Physical Review Letters 121, 056601 (2018) [PRL Cover page].

This research is supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant DMR-1420645.

Electron tunneling across a ferroelectric tunnel junction with strontium titanate (SrTiO₃) as a barrier layer for two polarization orientations (pointing to left – top panel and pointing to right – bottom panel). Color contrast indicates the amplitude of electron wave propagating from left to right (red – high; blue – low). The antisite TiSr defect enhances electron transmission across the junction which is seen from the red contrast on that site, indicating the enhanced amplitude for one polarization state but not for the other.